The present invention relates to a burglar alarm device for a vehicle, and in particular to the burglar alarm device that is suitable for a type of vehicle whose part of roof or entire roof are selectively opened and closed or detachable, or to a type of vehicle whose roof is fixed and whose part of roof or entire roof are made of a radio-wave transmittable material.
Conventionally, the burglar alarm device for a vehicle is known, which comprises the motion sensor (the sensor to detect an unauthorized person intruding into the vehicle compartment) to transmit ultrasonic waves or infrared rays continuously or periodically and receive such waves reflected in the vehicle compartment, and the warning means for executing alarming when a specified change in the reflected waves received by the motion sensor occurs in the alert state after the door lock or the like.
In the above-described burglar alarm device for a vehicle, it is also known that the motion sensor comprised of the ultrasonic-wave generator and the ultrasonic-wave receiver is provided at the center of the front header of the vehicle so as to detect the unauthorized person intruding into the vehicle compartment (for example, see U.S. Pat. No. 6,198,385).
Meanwhile, recently the radio-wave type of motion sensor using the radio wave that a non-metal member transmits has been developed. Accordingly, the use of this type of motion sensor can improve the burglar alarm function, for example, by hiding the motion sensor in the front header of the vehicle that is covered with a trim of the non-metal member.
Herein, in the case where the radio-wave motion sensor is, for example, provided at the center of the front header of the so-called open car whose roof is selectively opened and closed, the radio wave that has been transmitted by the motion sensor in a rearward and downward direction of the vehicle and then reflects at metal members, such as a seat frame of a seat cushion or a floor panel, goes upward beyond a roof position of the vehicle when the roof is in the open state. Also, even when the roof of the open car is closed, if the roof is made of the non-metal member, i.e., the radio-wave transmittable material, the reflected radio wave may go upward passing through and beyond the closed roof of the vehicle. In this case, there is a concern that the motion sensor would mistakenly detect other objects, such as birds or person's hands existing above the roof, as the above-described authorized person intruding into the vehicle compartment. Namely, the above-described radio wave going upward beyond the roof of the vehicle would cause a detection error by the motion sensor. Accordingly, there may be a problem of deterioration of the detection of the motion sensor.
In the case where the motion sensor is provided inside the side door, meanwhile, there may be a problem that the motion sensor would receive damages from the impact of the door opening/closing or from the water intruding into the door.